Symptomatic bursa formation with osteochondromas.

Two cases of bursa formation in association with osteochondromas are presented. This condition may be confused radiographically and clinically with malignant transformation of the cartilage cap. Ultrasound examination on one of the patients proved helpful in arriving at the correct preoperative diagnosis. Ultrasonography was also helpful to the surgeon with regard to size and extent of the bursa.     

Image editing with Adobe Photoshop 6.0.

The authors introduce Photoshop 6.0 for radiologists and demonstrate basic techniques of editing gray-scale cross-sectional images intended for publication and for incorporation into computerized presentations. For basic editing of gray-scale cross-sectional images, the Tools palette and the History/Actions palette pair should be displayed. The History palette may be used to undo a step or series of steps. The Actions palette is a menu of user-defined macros that save time by automating an action or series of actions. Converting an image to 8-bit gray scale is the first editing function. Cropping is the next action. Both decrease file size. Use of the smallest file size necessary for the purpose at hand is recommended. Final file size for gray-scale cross-sectional neuroradiologic images (8-bit, single-layer TIFF [tagged image file format] at 300 pixels per inch) intended for publication varies from about 700 Kbytes to 3 Mbytes. Final file size for incorporation into computerized presentations is about 10-100 Kbytes (8-bit, single-layer, gray-scale, high-quality JPEG [Joint Photographic Experts Group]), depending on source and intended use. Editing and annotating images before they are inserted into presentation software is highly recommended, both for convenience and flexibility. Radiologists should find that image editing can be carried out very rapidly once the basic steps are learned and automated.     

Image archival technologies.

A typical radiology department can create many gigabytes of image data per day and as much as 1 terabyte of data per year. Archiving and accessing this much data are substantial problems. One solution is data compression, which decreases data storage requirements and increases the rate of data transfer; however, standards are not yet available. Other solutions involve improvements in archival media. Jukebox subsystems allow automated access to multiple units. Digital magnetic tape, the standard medium, can store large amounts of information and enables easy updates or replacements; more practical technologies have been introduced in recent years. Digital videotape allows storage of digital video data and features a high rate of data transfer. Optical disks, now the preferred permanent archival medium, have a large storage capacity and provide excellent long-term stability. Optical tape is also being investigated as a solution to the archiving dilemma. Which technology to choose depends on many factors, including needs of the institution and the cost, stability, transfer time, and storage capacity of the system.     

Image reconstruction--a tutorial.

This paper is written for physicians and presents basic principles of image reconstruction in nuclear medicine. Both analytical and iterative methods are discussed without rigorous mathematics.     

Image comparison techniques for use with megavoltage imaging systems.

In this paper we describe software facilities for enabling patient positioning studies using the megavoltage imaging system developed at the Royal Marsden Hospital and Institute of Cancer Research. The study focuses on the use of the system for three purposes: patient position verification (by comparing images taken at treatment simulation with megavoltage images taken at treatment time); reproducibility studies (by analysing a set of megavoltage images); and set-up correction (by adjusting the set-up until the megavoltage image obtained at treatment registers with the simulation image). The need is discussed for suitably presented simulator images, a method of determining field boundaries and the possibility of delineating soft-tissue interfaces. Several algorithms of different types, developed specifically for the purpose of intercomparison of planar projection images, are presented. The techniques employed and their usefulness, in both the qualitative and the quantitative sense, are discussed. The results are presented of a phantom and clinical study, to evaluate the rigour and reproducibility of the algorithms. These results indicate that measurements can be made to an accuracy of about 1-2 mm, with a similar value for interobserver reproducibility for the best image comparison techniques available.     

Signal formation in echo-shifted sequences.

Echo shifted (ES) gradient-recalled echo sequences (whose TE > TR) have found important applications in fMRI and MR thermometry since their introduction. The technique increases T *(2) weighting in BOLD imaging and temperature change sensitivity in phase-based temperature imaging compared to FLASH sequences. Yet, inconsistent observations have previously been reported when variants of this technique were used in various MRI experiments. Previous understanding of the ES sequences (the "FLASH-like" postulation) was not sufficient to explain these observations. This work provides an in-depth study on the various ES sequences. It was found that there are two types of ES sequences: ES-FLASH that spoils coherent transverse magnetization and ES-GRE, which is based on SSFP signals. A signal expression was derived for the clinically popular TR-periodic ES-GRE sequence with one echo shift. This signal expression reduced to the "FLASH-like" postulation under certain conditions. The new knowledge about the echo formation mechanism in ES sequences helps explain the experimental observations previously reported. Moreover, the resonance offset angle based analysis demonstrates an elegant methodology to analyze short TR imaging sequences. Magn Reson Med 42:864-875, 1999.     

Recompression during decompression and effects on bubble formation in the pig

INTRODUCTION: There is a relationship between gas bubble formation in the vascular system and serious decompression sickness. Hence, control of the formation of vascular bubbles should allow safer decompression procedures. METHODS: There were 12 pigs that were randomly divided into an experimental group (EXP) and a control group (CTR) of 6 animals each. The pigs were compressed to 500 kPa (5 ATA) in a dry hyperbaric chamber and held for 90 min bottom time breathing air. CTR animals were decompressed according to a modified USN dive profile requiring four stops. EXP followed the same profile except that a 5-min recompression of 50 kPa (0.5 ATA) was added at the end of each of the last three decompression stops before ascending to the next stop depth. RESULTS: All CTR animals developed bubbles, compared with only one animal in EXP. The number of bubbles detected during and after the dive was 0.02 +/- 0.02 bubbles x cm(-2) in CTR, while the number of bubbles detected in EXP were 0.0009 +/- 0.005 bubbles x cm(-2); the difference was highly significant. CONCLUSION: By brief recompression during late decompression stops, the amount of bubbles was reduced. Our findings give further support for a gas phase model of decompression.     

Image quality in cranial computed tomography.

Image quality in cranial computed tomography (CT) was evaluated with phantom and patient studies on both a first (single beam) and a second (multiple beam) generation scanner. When comparable radiation doses were used, there were only minor differences in resolution, low contrast detectability, and noise level. The pattern of noise relative to the size of the area in which it was measured was somewhat different. On patient studies, no differences were found when contrast-material-filled vessel visibility and gray--white matter distinction were analyzed. A lesion was obscured by streak artifacts in one scanner in one of 22 patients scanned on both machines. The major factor in image quality as seen in the two scanners seemed to be in the production of artifacts. This was apparent in artifacts from motion, high contrast discontinuities, beam hardening, and edge enhancement. Multiple factors must be considered in assessing CT image quality. In particular, further studies to quantitatively evaluate noise quality and artifact production are needed.     

Image reconstruction for echo planar imaging with nonequidistant k-space sampling.

Echo planar imaging is characterized by scanning the 2D k-space after a single excitation. Different sampling patterns have been proposed. A technically feasible method uses a sinusoidal readout gradient resulting is measured data that does not sample k-space in an equidistant manner. In order to employ a conventional 2D-FFT image reconstruction, the data have to be converted to a cartesian grid. This can be done either by interpolation or alternatively by a generalized transformation. Filtering methods are described to minimize ghosting artifact that is typical in echo planar imaging. Results both from computer simulation and from experiments will be presented. Experimental images were obtained using a 2-T whole-body research system.     

Assessing the effects of body weight on subchondral bone formation with quantitative 18F-sodium fluoride PET

Annals of Nuclear Medicine - The aim of this study was to quantify subchondral bone remodeling in the elbows, hands, knees, and feet using volumetric and metabolic parameters derived from...     

Blood clot formation in angiographic catheters. In vitro tests with various contrast media

Human blood was injected into angiographic catheters filled with contrast media or flushing media. The catheters were allowed to stand at 37 degrees C for 10, 20 or 30 min. Physiologic saline was then injected through the catheters, the catheter contents were shaken and filtered, and any clots were identified. Diatrizoate, ioxaglate, iohexol, iopamidol and iopromide were tested. Physiologic and heparinized saline were used as controls. At 10 min, clots were found in 65 per cent of the catheters filled with physiologic saline, in 25 per cent with non-ionic media, in 19 per cent with heparinized saline, and in 4 per cent with ionic contrast media. At 30 min, all catheters with physiologic saline, 85 per cent with non-ionic contrast media, 46 per cent with heparinized saline and 23 per cent with ionic contrast media contained a clot. Although all the contrast media were anticoagulants, a more careful angiographic technique is needed for non-ionic media. All the non-ionic agents showed equal results. Physiologic saline without heparin is not suitable for flushing during angiography.     

The effects of incomplete breath-holding on 3D MR Image Quality

The purpose of this study was to investigate how fast three-dimensional (3D) MR image quality is affected by breath-holding and to develop an optimal breath-holding strategy that minimizes artifact in the event of an incomplete breath-hold. A computer model was developed to study variable-duration breath-holds during fast 3D imaging. Modeling was validated by 3D gradient-echo imaging performed on 10 volunteers. Signal-to-noise ratio (SNR) and image blur were measured for both simulated and clinical images. Insights gained were applied to clinical 3D gadolinium-enhanced MR angiography. Breath-holding significantly improved abdominal 3D MR image quality. Most of this benefit could be achieved with a breath-hold fraction of 50% if it occurred during acquisition of central k space. Breath-holding during peripheral k-space acquisition, however, had no significant benefit. Respiratory motion artifact on fast 3D MRI occurring when a patient fails to suspend respiration for the entire scan duration can be minimized by collecting central k space first (centric acquisition) so that premature breathing affects only the acquisition of peripheral k space.     

Layer formation in narrow beam rotation radiography.

The layer formation in rotation narrow beam radiography is analysed mathematically. It is shown that the blurring, and consequently the layer formation, is due primarily to the width of the beam; no blurring and no layer formation occur if the beam is of negligible width. The blurring is significantly affected by the magnification factor in the specific central projection typical of narrow beam rotation methods, where the rotation centre serves as an imaginary focus.